<!DOCTYPE html>
<html lang="cn">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<style>
	*{
		margin: 0;
		padding: 0;
	}
	.wrap,.circle,.percent{
		position: absolute;
		width: 200px;
		height: 200px;
		border-radius: 50%;
	}
	.wrap{
		top:50px;
		left:50px;
		background-color: #ccc;
	}
	.circle{
		box-sizing: border-box;
		border:20px solid #ccc;
		clip:rect(0,200px,200px,100px);
	}
	.clip-auto{
		clip:rect(auto, auto, auto, auto);
	}
	.percent{
		box-sizing: border-box;
		top:-20px;
		left:-20px;
	}
	.left{
		transition:transform ease;
		border:20px solid blue;
		clip: rect(0,100px,200px,0);
	}
	.right{
		border:20px solid blue;
		clip: rect(0,200px,200px,100px);
	}
	.wth0{
		width:0;
	}
	.num{
		position: absolute;
		box-sizing: border-box;
		width: 160px;
		height: 160px;
		line-height: 160px;
		text-align: center;
		font-size: 40px;
		left: 20px;
		top: 20px;
		border-radius: 50%;
		background-color: #fff;
		z-index: 1;
	}
	</style>
	<script src="http://apps.bdimg.com/libs/zepto/1.1.4/zepto.min.js"></script>
</head>
<body>
<div class="wrap">
	<div class="circle">
		<div class="percent left"></div>
		<div class="percent right wth0"></div>
	</div>
	<div class="num"><span>0</span>%</div>
</div>
</body>
<script>
	var percent=0;
	var loading=setInterval(function(){
		if(percent>100){
			percent=0;
			$('.circle').removeClass('clip-auto');
			$('.right').addClass('wth0');
		}else if(percent>50){
			$('.circle').addClass('clip-auto');
			$('.right').removeClass('wth0');
		}
		$('.left').css("-webkit-transform","rotate("+(18/5)*percent+"deg)");
		$('.num>span').text(percent);
		percent++;
	},200);
</script>
</html>
